1. Field of the Invention
The present invention relates to a manufacturing method of common mode filters and a structure of the same, especially to a common mode filter that provides more stable support by a composite substrate and connects inductive coils with external electrodes by wafer scale packaging techniques for minimization of the volume. Once the common mode filters are of compact size, they can be mass-produced, the cost is reduced and the defect rated is decreased. At the same time, the connection and conduction between the inductive coils and the external electrode are more convenient and easier. The common mode filters are of higher practical value and the manufacturing method thereof is novel.
2. Description of Related Art
Due to compact design of various electronics such as mobile phones, cameras, etc. for easy carrying, electronic components are required to have compact volume, with high performance and high frequency. The manufacturing of the minimized components is difficult. As to small-sized common mode filters, as disclosed in U.S. Pat. No. 7,023,299 B2 published on Apr. 4, 2006, a thin-film common mode filter includes a pair of magnetic plates, and upper/lower coil conductors that are formed between the magnetic plates, spirally wound in the magnetic plate surface direction, and overlapped each other, and upper/lower lead conductors. One ends of the upper/lower lead conductors are connected electrically to one ends in centers of the upper/lower coil conductors respectively, and extended to external portions across these coil conductors. The other ends of the upper/lower lead conductors are connected to upper/lower lead drawing terminals respectively. And each of the lower lead/coil drawing terminals and the upper coil/lead drawing terminals has a structure in which at least two of conductor layers that are patterned into the upper/lower lead conductors and the upper/lower coil conductors are stacked and brought into conduction with each other.
Although the above common mode filter provides expected effects, it still has problems. In practice, a plurality of common mode filters are arranged in a sheet during manufacturing processes first and are cut into individuals by cutting tools. Then external electrodes are produced on outer sides of each common mode filter by silver dipping. However, a magnetic composite substrate of the common mode filter is easy to get cracked during clamping of manufacturing processes due to weak strength. And during the cutting process, the common mode filters are easy to get damaged and this results in additional cost/loss. Furthermore, the external electrodes are produced by silver dipping and are connected to leading-out terminals after cutting. For volume minimization, the relative size of the common mode filer is about 1.0 mm×0.5 mm×0.4 mm. Thus the formation of the external electrodes requires high precision techniques. Moreover, reliability of the external electrode is a problem. There is room for improvement and a need to provide a manufacturing method of common mode filters and a structure of the same having higher practical value.